Field of the Invention
The present invention relates to a machine control panel, and more particularly, to a machine control panel compliant with the safety standards.
Description of the Related Art
An example of a conventional machine control panel will be described with reference to FIG. 3.
As shown in FIG. 3, a machine control panel 12 is connected to a numerical controller 10 by a bus 18. Since the machine control panel 12 comprises only a plurality of single-contact key switches 14 and one communication circuit 16, it is difficult to categorize signals of the key switches 14 into two systems. In order to make the machine control panel 12 comply with the safety standards, signals related to the hold-to-run control of jog buttons, among other switches on the machine control panel 12, should first be categorized into two systems.
Accordingly, as shown in FIG. 4, the single-contact key switches on the machine control panel are replaced with a double-contact switch (hold-to-run) 28 such that key switch signals can be categorized into two systems by inputting signals from the switch 28 to communication circuits 22 and 26 of independent I/O units 20 and 24. Further, safety-related signals are transmitted from the communication circuits 22 and 26 of the I/O units 20 and 24 to the numerical controller 10 through buses 30. The signals received by the numerical controller 10 are compared so that they can be made to comply with the safety standards by monitoring the integrity of the safety function.
As shown in FIG. 5, moreover, a double-contact enable switch 32 may be provided, and signals from the double-contact enable switch 32 are input to the communication circuits 22 and 26 of the independent I/O units 20 and 24 so that these signals may be categorized into two systems. Further, by using the double-system enable switch 32 in combination with the key switches 14 of the machine control panel 12, it is possible to make these switches 32, 14 comply with safety standards. For example, the enable switch 32 may be configured so that signals of the key switches 14 on the machine control panel 12 are enabled only when the enable switch 32 is depressed.
The safety-related signals include input signals for external emergency stop and the like and output signals for power interruption and the like, as well as the input signals related to the hold-to-run control. The input signals for emergency stop and the like can be made to comply with the safety standards in the same method as in FIG. 4. To make the output signals for power interruption and the like comply with the safety standards, as shown in FIG. 6, it is necessary to transmit the safety-related signals from the numerical controller 10 to the communication circuits 22 and 26 of the independent I/O units 20 and 24 and output signals of two systems from the communication circuits 22 and 26 to power interruption means 34.
Japanese Patent Application Laid-Open No. 11-16132 discloses a technique for comparing and monitoring signals in a numerical controller. Buses capable of transmitting safety-related signals are described in “Ursprünglich veröffentlicht in deutscher Sprache von Hüthig GmbH & Co KG, Heidelberg, Bundesrepublik Deutshland unter dem Titel Reinert, Schafer (Hrsg,): Sichere Bussysteme fur die Automation. Copyright 2001”. Further, a method of complying with the safety standards using an enable switch is disclosed in “Safety Standards EN12417”.
There is a problem that I/O units and switches for a dual-system configuration must be separately provided to make a noncompliant machine comply with the safety standards. There is also a problem that the operability of a machine control panel inevitably varies if an enable switch and key switches are used in combination.